Computer systems are fundamentally comprised of subsystems for storing and retrieving data, manipulating data, and displaying results. Nearly all computer systems today use optical, magnetic or magneto-optical storage media to store and retrieve the bulk of a computer system's data. Successive generations of ever more powerful microprocessors, and increasingly complex software applications that take advantage of these microprocessors, have driven the storage capacity needs of systems higher and have simultaneously driven read and write performance demands higher. Magnetic storage remains one of the few viable technologies for economically storing large amounts of data with acceptable read and write performance.
There are basic components common to nearly all magnetic hard disk drives. A hard disk drive typically contains one or more disks clamped to a rotating spindle, heads for reading and writing information to the surfaces of each disk, and an actuator assembly utilizing linear or rotary motion for positioning the head for retrieving information or writing information to a location on the disk. A rotary actuator is a complex assembly that couples a slider on which the head is attached to a pivot point that allows the head to sweep across the surface of the rotating disk.
The disks and the slider can be extremely smooth, and strong adhesive forces can prevent disks from rotating during a “power-on” cycle if the slider is landed on the disk surface. To prevent this phenomenon, modern hard disk drives typically use one of two solutions: (1) a narrow area close to the disk center is textured using a laser to create a special landing zone on the disk, or (2) a load-unload ramp is positioned either adjacent to the disk or just over the disk surface. Where a special landing zone is used, a spiral of tiny laser bumps can be created which increases a disk's roughness, decreases adhesion, and allows the slider to land and take-off from the landing zone. Where a load-unload ramp is used, the suspension is moved beyond the disk area and slides onto the ramp thus parking the head. Both parking on the ramp and landing on the landing zone can increase the drive's non-operational shock resistance and prevent accidental damage during transportation. To prevent damage to the head such as during “power-down” and “power-on” cycles, the velocity of the head must be controlled, particularly when loading from and unloading to a ramp. Current methods for controlling the velocity of the head can be inaccurate, particularly during transitions from low to high current (for example during a “power-on” cycle).